Author Information

Derek Phan

Background

Determination of the heart rate corrected QT interval (QTc) is the basis for accurate ECG diagnosis of long QT syndrome (LQTS). The various commonly used formulas for heart rate correction have not been systematically evaluated in infants and young children.

Methods

Digital recordings of standard 12-lead ECGs were obtained from 702 children ≤ 6 years old with hearing loss who participated in a study of ECG screening for LQTS. The RR and QT intervals were digitally measured with a 4X zoom, each by 2 independent reviewers. QT intervals were then corrected for heart rates by use of the Bazett, Fridericia, Hodges, and Framingham formulas. QTc intervals (y-axis) were plotted against RR intervals (x-axis), and slopes of regression lines were compared. The closer the slope is to zero, the better heart rate correction across different heart rates.

Results

The mean age of the subjects was 2.3±1.7 years, with 230 (33%) <1 year. Heart rates ranged from 76 to 188 bpm (123±19).

Formula

Mean QTc

QTc Standard Deviation (SD)

Slope of QTc-RR Regression

QTc 2 SD above mean

Bazett

412

18

0.0046

448

Fridericia

366

19

0.125

403

Hodges

401

17

−0.128

435

Framingham

289

26

0.291

342

For infants <1 year old, Bazett Formula also achieved the most consistent heart rate correction across heart rates ranged from 99 to 188 bpm (139±17), with near zero slope in QTc-RR plot (−0.01). The mean QTc by Bazett formula was 412±19 ms, and 2SD threshold 450 ms

Conclusions

The Bazett formula provided the best heart rate correction formula across a wide range of heart rates in infants and young children. The upper limit of QTc 450 ms remains the statistical threshold for consideration of a diagnosis of the prolonged QTc in infants and young children

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